Magnetization reversal in trained exchange biased multilayers

Abstract

FM magnetization may be collinear (responsible for nonuniform reversal) ornoncollinear (responsible for uniform reversal) to the direction of the applied field inferromagnetic–antiferromagnetic (FM–AF) exchange-biased systems depending upon thenumber of field cycles it has undergone. Usually noncollinearity sets in right after the firstfield cycle, i.e. when the system is in the trained state. Here we show that in case ofpolycrystalline multilayers (MLs) of continuous AF–FM interfaces (ML-C), e.g. in[Co/CoO]20, this collinearity of the FM magnetization remains not only in the untrained state but evenin the trained state as each FM layer in the ML remagnetizes symmetrically for both fieldbranches via the nonuniform mode only. Thus the state of magnetization can remainvirtually unaffected by repeated field cycling, and this can be exploited in building stablestate spin-valve systems.